Question: Suppose the diameter of a circle is ${8}$. What is its area?
Answer: ${d = 8}$ ${K = 16\pi}$ First, find the radius: $r = d/2 = {8}/2 = {4}$ Now find the area: $K = \pi r^2$, so $K = \pi \cdot {4}^2 = {16\pi}$.